1. Field of the Invention
The present invention relates to a stator for an alternator driven by an internal combustion engine, for example, and to a method for manufacturing the stator, and in particular, relates to a stator for an alternator and a method for the manufacture thereof in which the stator is provided with a stator coil constructed by installing coil wires having a flat cross section formed into a predetermined shape into a stator core, and welding together end portions of the coil wires.
2. Description of the Related Art
FIG. 38 is a cross section showing the construction of a generic alternator.
The conventional alternator includes: a Lundell-type rotor 7 mounted so as to rotate freely by means of a shaft 6 within a case 3 composed of an aluminum front bracket 1 and an aluminum rear bracket 2; and a stator 8 secured to the inner wall of the case 3 so as to cover the outer circumference of the rotor 7.
The shaft 6 is rotatably supported by the front bracket 1 and the rear bracket 2. A pulley 4 is secured to one end of the shaft 6 to enable rotational torque from an engine to be transmitted to the shaft 6 by means of a belt (not shown).
Slip rings 9 for supplying electric current to the rotor 7 are secured to the other end of the shaft 6, and a pair of brushes 10 are housed in a brush holder 11 and disposed within the case 3 so as to slide in contact with the slip rings 9. A regulator 18 for regulating the magnitude of an alternating voltage generated in the stator 8 is affixed by adhesive to a heat sink 17 attached to the brush holder 11. A rectifier 12 electrically connected to the stator 8 for converting the alternating voltage generated in the stator 8 into direct current is mounted within the case 3.
The rotor 7 includes: a rotor coil 13 for conducting electric current and generating magnetic flux; and a pair of pole cores 20, 21 disposed so as to cover the rotor coil 13, magnetic poles being formed in the pair of pole cores 20, 21 by the magnetic flux generated by the rotor coil 13. The pair of pole cores 20, 21 are made of iron, each has a plurality of claw-shaped magnetic poles 22, 23 projecting from an outer circumferential edge thereof spaced at even angular pitch circumferentially, and the pole cores 20, 21 are secured to the shaft 6 facing each other so that the claw-shaped magnetic poles 22, 23 intermesh. In addition, fans 5 are secured to both axial ends of the rotor 7.
The stator 8 includes: a stator core 15; and a stator coil 16 composed of wire wound around the stator core 15 and having coil end groups 16a and 16b extending from the axial ends of the stator core 15.
In an alternator constructed in this manner, current is supplied to the rotor coil 13 from a battery (not shown) by means of the brushes 10 and the slip rings 9, and magnetic flux is generated. The claw-shaped magnetic poles 22 of one pole core 20 are polarized with north-seeking (N) poles by the magnetic flux, and the claw-shaped magnetic poles 23 of the other pole core 21 are polarized with south-seeking (S) poles. At the same time, the rotational torque of the engine is transmitted to the shaft 6 by means of the belt and the pulley 4, and the rotor 7 is rotated. Thus, a rotating magnetic field is imparted to the stator coil 16 and electromotive force is generated in the stator coil 16. This alternating electromotive force is converted into direct current by means of the rectifier 12, its magnitude is regulated by the regulator 18, and the battery is recharged.
Next, the construction of a conventional stator 8 will be explained in detail with reference to FIGS. 39 and 40. FIG. 39 is a perspective showing a coil segment constituting part of a conventional stator coil, and FIG. 40 is a perspective of part of a conventional stator viewed from the front end.
As shown in FIG. 39, the coil segments 30 functioning as coil wires are formed into a predetermined shape by cutting insulated copper wire material having a flat cross section into predetermined lengths which constitute coil members 29 and applying a bending process to the short, cut coil members 29. More specifically, the coil segments 30 are composed of a pair of straight portions 30a in which the longitudinal direction of the cross sections of each are generally parallel to each other, and a turn portion 30b which connects the straight portions 30a in a general V shape in which the longitudinal direction of the cross section is twisted at approximately 180° at an apex portion, forming an overall U shape.
In FIG. 40, the stator core 15 is formed into a cylindrical shape, a number of teeth 15a having a generally rectangular cross-sectional shape are disposed at even angular pitch circumferentially so as to extend radially inwards, and slots 15b for housing the coil are formed between the teeth 15a. The grooves of the slots 15b are parallel to an axial direction and are open on an inner circumferential side. Insulating paper 19 is housed in each of the slots 15a. In this case, the rotor has 12 poles, and the stator 8 has thirty-six slots 15b, making the number of slots per pole per phase equal to one.
These coil segments 30 are inserted two at a time from a rear end of the stator core 15 into pairs of slots 15b three slots apart such that the height of the turn portions 30b is uniform. Thus, four straight portions 30a are housed in each of the slots 15b such that the longitudinal direction of the cross sections of the straight portions 30a are aligned in a radial direction so that the straight portions 30a line up in a row radially. Free end portions 30c of the coil segments 30 projecting from each of the slots 15b are each bent circumferentially in the vicinity of the end of the stator core 15, then the free end portions 30c are each additionally bent such that the longitudinal direction of the cross sections thereof are each aligned radially and the free end portions 30c are parallel to the axial direction. The free end portions 30c of coil segments 30 projecting from slots 15b three slots apart are stacked radially and welded together, constituting three winding phase groups having four turns in each phase. The stator coil 16 is prepared by connecting the three winding phase groups constructed in this manner into a Y connection, for example.
The turn portions 30b of the coil segments 30 in the rear-end coil end group 16b of the stator coil 16 are constructed so as to be arranged circumferentially so as to line up radially in two rows at the rear end of the stator core 15. On the other hand, the front-end coil end group 16a is constructed such that inner circumferential joint portions 31 formed by radially stacking and welding the free end portions 30c of the coil segments 30 projecting from the first position (hereinafter called the first address) from the inner circumferential side of the slots 15b and the free end portions 30c of the coil segments 30 projecting from the second position (hereinafter called the second address) from the inner circumferential side of the slots 15b three slots away, and outer circumferential joint portions 32 formed by radially stacking and welding the free end portions 30c of the coil segments 30 projecting from the third position (hereinafter called the third address) from the inner circumferential side of the slots 15b and the free end portions 30c of the coil segments 30 projecting from the fourth position (hereinafter called the fourth address) from the inner circumferential side of the slots 15b three slots away are arranged circumferentially so as to line up radially in two rows.
A method for manufacturing the conventional stator 8 will now be explained with reference to FIGS. 41 to 48.
First, flat insulated copper wire material is cut into predetermined lengths using a nipper or the like to obtain coil members 29, as shown in FIG. 41.
Then, coil segments 30 functioning as coil wires shown in FIG. 42 are obtained by forming a coil member 29 into a U shape by a bending process.
Then, the coil segments 30 are inserted two at a time into pairs of slots 15b three slots apart such that the height of the turn portions 30b is uniform. At this time, four straight portions 30a are housed in each slot 15b such that the longitudinal direction of the cross sections of the straight portions 30a are aligned in the radial direction so as to line up in a row radially. The free end portions 30c of the coil segments 30 projecting from each of the slots 15b are each bent circumferentially in the vicinity of the end of the stator core 15, then the free end portions 30c are each additionally bent such that the longitudinal direction of the cross sections thereof are each aligned radially and the free end portions 30c are parallel to the axial direction. Thus, the free end portions 30c of the two coil segments 30 projecting from the first and third addresses from the inner circumferential side of a slot 15b and the free end portions 30c of the two coil segments 30 projecting from the second and fourth addresses from the inner circumferential side of a slot 15b three slots away are lined up in the radial direction as shown in FIGS. 43 and 44.
Next, the ends of the four coil segments 30 are held by lining up clamping jigs 27 in a straight line and bringing the tips of the jigs 27 together, as shown in FIGS. 45 and 46. Then, the free end portions 30c of the two coil segments 30 on the inner circumferential side are fused and joined together by tungsten-inert gas (TIG) welding using an arc. The free end portions 30c of the two coil segments 30 on the outer circumferential side are fused and joined together in the same way by TIG welding using an arc. Thus, inner circumferential joint portions 31 and outer circumferential joint portions 32 are obtained as shown in FIGS. 47 and 48. The three winding phase groups having four turns in each phase are obtained by welding each of the free end portions 30c together. Moreover, heat generated during welding is transferred through the jigs 27 to a radiating jig 28 and radiated to prevent the coating on the coil segments 30 from being burned.
The stator coil 16 is prepared by connecting the three winding phase groups prepared in this manner into a Y connection, for example.
In this conventional stator for an alternator, short coil members 29 obtained by cutting wire material using a nipper or the like, are formed into U-shaped coil segments 30 by a bending process. As shown in FIG. 41, bulges A and burrs B caused by cutting arise on side portions of the cross sections of these coil members 29. Because the bulges A and burrs B extend beyond the profile of the coil members 29, when the coil segments 30 are being inserted into the slots 15b, the bulges A catch and make it difficult to insert the coil into the slots, and the burrs B damage the insulating paper 19 giving rise to insulation defects. Thus, one problem has been reduced productivity and reliability.
Because the insulation coating on the free end portions 30c of the coil segments 30 is not removed, welding deteriorates, giving rise to dislodgement of the joint portions due to vibrations from the engine, etc., causing problems which reduce reliability.
Because the outer dimension of the free end portions 30c of the coil segments 30 is not reduced, the free end portions 30c which are joined in the coil end group 16a are arranged in close contact in one row radially, leaving little space for welding. As a result, when welding the free end portions 30c of the two coil segments 30 on the inner circumferential side, for example, there is a risk that the heat of welding will be transferred to the free end portions 30c of the coil segments 30 on the outer circumferential side and weld them to the free end portions 30c on the outer circumferential side as well, reducing productivity. In addition, because it is difficult to concentrate the arc on the interface between the free end portions 30c of the two coil segments 30 being welded and the fused surface area is reduced, sufficient weld strength cannot be obtained, giving rise to dislodgment of the joint portions due to vibrations from the engine, etc., thus causing problems which reduce reliability. Furthermore, electrical resistance is increased in the joint portions, increasing the amount of heat generated by the output current during power generation, causing reduced output due to temperature increases.
Furthermore, if welding time is increased in order to ensure sufficient fused surface area, the weld bead formed on the joint portion becomes too large, which later results in the occurrence of layer shorts due to vibration, thus reducing reliability.